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Flexion, compression leading cause of healthy disc herniation
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Flexion and an elevated rate of compression are the two most common factors in the herniation of healthy lumbar discs at a microstructural level.
Researchers looked at 72 healthy, mature, female ovine lumbar discs and analyzed the results when the lumbar motion segments were compressed to failure. Testing was halted when stages ranging from initial wall tearing through to facet fracture were observed in the discs.
Two different compression velocities — a low velocity of 2 mm/min and a high velocity of 40 mm/min — were employed on each disc.
The researchers found that approximately 50% of the discs undergoing the high velocity experienced annulus or annulus-endplate junction failure. The remaining high-velocity discs failed via endplate fracture with no visible wall damage.
The load to induce disc plate failure for flexion was on average 18% lower than the load to induce endplate fracture, according to the researchers.
“Disc wall failure in healthy motion segments requires both flexion and an elevated rate of compression. Damage is initiated in the mid-then-outer annular fibers; this a likely consequence of the higher strain burden in these same fibers arising from endplate curvature,” the researchers wrote.
Disclosure: AO Foundation grant funds were received in support of this work.
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Wade KR. Spine. 2014. doi:10.1097/BRS.0000000000000262.
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